As immune regulation may consist of a network of idiotypes and anti-idiotypes, it becomes important to determine the molecular identity of a given idiotype and the degree of heterogeneity within an idiotypic system. The major cross-reacting idiotype in strain A/J mice immunized with para-azophenylarsonate is heritable and was thought to be a homogeneous phenotype encoded by germ-line structural genes. In light of the fact that (1) DNA structural studies have indicated that variable regions are controlled by more than one gene, (2) serological heterogeneity is found among hybridoma proteins bearing idiotypes and (3) preliminary studies in this laboratory and that of our collaborators have indicated that hybridomas bearing the Ars idiotype are serologically and structurally microheterogeneous, it is necessary to reexamine the structure of this major CRI, which has implications for the identity of the T-cell receptor for antigen and mechanisms responsible for the occurrence of a predominant idiotype. Therefore, the complete V region amino acid sequence of heavy and light chains from CRI+ hybridoma proteins will be examined. Structural studies on a second set of CRI+ hybridomas which do not bind antigen, induced following immunization with anti-idiotype, provide an additional opportunity for studying the diversity and regulation of the major CRI. In addition, the V regions of a family of A/J hybridoma proteins bearing a second idiotype (Id36-60) structurally and serologically distinct from the predominant idiotype will be determined. The results of sequence analyses will be correlated with serological studies employing monoclonal anti-idiotypic reagents which have detected differences among idiotypes borne by molecules bearing the CRI. Chain recombination will also be used to assess the contributions of heavy and light chains in these various idiotypic systems. Results of structural analyses will be correlated with determination of the affinity and fine specificity for related haptens of each hybridoma. The results of the protein sequence studies will be correlated with determination of the DNA sequence (to be done by collaborators, Gefter et al.) in an effort to examine the mechanism for diversification in these two idiotype families.